Cocaine and amphetamine regulated transcript (CART) peptide is an endogenous peptide which appears to have psychostimulant-like properties and may be involved in the actions of cocaine and other psychostimulants. Understanding the effects of CART peptide is important because it will give insight into the addiction process and will contribute to the goal of developing a pharmacological treatment for cocaine and amphetamine addiction. The purpose of this study is to more fully characterize the behavioral and neurochemical psychostimulant-like actions of CART peptide and its interaction with cocaine. This includes determining 1) if behavioral sensitization or tolerance occurs to repeated CART injections and if cross-sensitization occurs to cocaine; 2) if CART injection into the ventral tegmental area and nucleus accumbens increases extracellular dopamine concentrations in the nucleus accumbens like psychostimulants do; and 3) if CART can modify cocaine self-administration. The researchers hypothesis is that CART will act in a similar manner as cocaine on these measures. By studying the behavioral and neurochemical effects of CART and it's interactions with cocaine, this project will yield a greater understanding of both the acute reinforcing mechanisms of cocaine and long-term changes that occur during chronic cocaine abuse. A greater understanding of the functions of CART may in turn lead to novel treatment strategies for psychostimulant abuse.